I. Field of the Invention
This invention relates to an improved hopper dryer for use in preheating and drying pelletized or granular resin.
II. Prior Art
In a conventional method for drying resin materials, such as pelletized resin, the pelletized resin materials are preheated to promote of softening and dissolving, and simultaneously heated air is blown into a hopper for drying in which pelletized resin materials are stored before the resin materials are fed into a molding machine.
However, according to such a conventional method, a large hopper tank is needed and the space required apt to be large. As a result, the sizes of the drying equipment becomes large as a whole, since the hopper is designed such that heated air is blown therein to dry the materials with the hopper filled with resin materials.
Further, since the conventional hopper is designed such that heated air is blown therein for drying from the underside thereof with the hopper filled with resin materials, it takes a long time to dry the resin materials, and what is worse a uniform drying condition can not be expected. In addition to the above mentioned drawbacks, dispersion in drying would arise depending on the up and down position in the hopper dryer in which resin materials are stored.
A hopper dryer comprising double concentric cylinders has been proposed to solve the above mentioned problems.
FIG. 4 illustrates the conventional type of hopper dryer having double cylinders. The main body 100 of the hopper dryer is constructed such that an inner wall 102 having a plurality of apertures 102a for the suction of heated air is disposed concentrically in an outer wall 101 having a plurality of apertures 101a for the suction of heated air. At the top portion of the inner wall 102 an air suction source such as a vacuum pump (not shown) is connected and a heater band 103 is provided around the external circumference of the outer wall 101. Resin materials 106 are stored in a hopper 105, disposed at the upper portion of the hopper dryer, and are fed into the space between the outer wall 101 and the inner wall 102 of the main body 100 and dried by the air heated by the heater band 103.
However, since the heater band 103 is provided at the periphery of the outer wall 101 in the above mentioned dryer, the space between the outer wall 101 and the inner wall 102 which forms a storage space for pelletized resin would be reduced if the equipment, as a whole is reduced in size.
Furthermore according to such a hopper dryer, it has disassembly and cleaning of the hopper presents troubles, especially when resin materials to be stored are exchanged frequently, since the dryer is constructed such that the heater band 103 is disposed outside of the outer wall 101.